1. Field of the Invention
The present invention relates to an LED light emitting apparatus in which LED chips are mounted on a substrate and a vehicle headlamp using the same.
2. Description of the Related Art
Enlarging LED chips (500 μm to 1 mm long on one edge) is propagated to allow a large current to flow for high light output and/or to cause them to be driven in low-current regions of high luminous efficiency by reducing a current density per area, and a plurality of pad electrodes for wire bonding are formed on a wide area of light emitting surface of such an LED chip for uniform current supply (Patent Documents 1, 2).
A conventional example 1 shown in FIG. 15 is an LED light emitting apparatus 210 in which four large LED chips 201 are mounted on a sub-mount substrate of a required minimum size for mounting the LED chips 201 in a row to form a single series circuit. Formed on a light emitting surface of the LED chip 201 are two pad electrodes 202 lying in corners of one edge and finger electrodes (whose illustration is omitted) which extend linearly from both the pad electrodes 202 so as to scatter on the light emitting surface. The sub-mount substrate is a wiring board or printed circuit board which is made up of a ceramic board 212 and five conductive patterns 213 which are formed on an upper surface of the circuit board. One LED chip 201 is disposed on each of lower four patterns, and the LED chips 201 so disposed are electrically and thermally joined to the corresponding patterns on their lower surfaces. Two wires 209, 209 are installed to extend, respectively, from the two pad electrodes 202, 202 of each LED chip 201 so as to be placed in bonding areas of the next upper conductive pattern 213 in FIG. 13 for bonding. The installing directions of the wires 209, 209 from the pad electrodes 202, 202 when viewed from thereabove are orthogonal moving-away directions relative to facing edges 201a, 201b of each LED chip 201 (directions in which the wires move away at right angles to the facing edges 201a, 201b. This will be true below). Because of this, a pattern width of the conductive pattern 213 where ends of the two wires 209, 209 are bonded is increased, leading to a problem that the size of the sub-mount substrate 211 is increased.
A conventional example 2 shown in FIG. 16 is an LED light emitting apparatus in which the conventional example 1 is arranged in double rows, that is, eight LED chips 201 are mounted on a sub-mount substrate 221 so as to be arranged in two rows to form two series circuits. An installing direction of wires 209, 209 is similar to that of the conventional example 1. An inter-chip-space is increased because wires from one row are aligned with wires from the other row between the two rows of LED chips 201 in an end-to-end fashion, leading to a problem that the size of the sub-mount substrate 221 is also increased.
A conventional example 3 shown in FIG. 17 is an LED light emitting apparatus 230 in which eight LED chips 201 are mounted on a base substrate 231 including receiving terminals for contact with feeding terminals of an illumination appliance so as to be arranged in two rows to form two series circuits. An installing direction of wires 209, 209 is similar to that of the conventional example 1. For example, two anode patterns 233a and one common cathode pattern 233c of conductive patterns 213 are extended from a lower edge or a mounting edge of the LED light emitting apparatus 230, and respective extended end portions are made to function as receiving terminals. The two anode patterns 233a are positioned at a left-hand edge and a center of the mounting edge, and the cathode common pattern 233c is positioned at a right-hand edge of the mounting edge. When the LED chips of the two circuits are driven at the same time, more current is caused to flow through the cathode common pattern 233c than each of the anode patterns 233a. Therefore, a voltage drop in the cathode common pattern 233c becomes large due to an internal resistance thereof. Consequently, the cathode common pattern 233c should be formed wider than each anode pattern 233a so as to reduce the internal resistance thereof. However, feeding terminals provided on a mounting holder of the illumination appliance are disposed at equal intervals, and their positions are determined and cannot be changed in many cases. In some cases, this prevents a sufficient extension of the width of the cathode common pattern 233c. Namely, even when attempting to extend the width of the cathode common pattern 233c disposed at the right-hand edge of the mounting edge, the cathode common pattern 233c must not be extended in such an extent that it contacts or overlaps the central feeding terminal 236, and hence, there is a limitation on the extension of the cathode common pattern 233c. 
A conventional example shown in FIG. 18 is a vehicle headlamp 240 which employs the LED light emitting apparatus 210 described in the conventional example 1. In this vehicle headlamp 240, the LED light emitting apparatus 210 of the conventional example 1 is mounted on a base substrate 241 with receiving terminals with its upper surface oriented upwards so that light is emitted upwards from the light emitting surfaces of the LED chips or to the peripheries thereof. A reflector 242 is provided at the rear (to the left in FIG. 18) of the LED light emitting apparatus 210 so as to extend around the LED chips 201 so that light emitted upwards or to the peripheries of the light emitting surfaces of the LED chips 201 is reflected to the front. Then, a forward illumination lens (whose illustration is omitted) is provided ahead of the LED light emitting apparatus 210 so as to collect the light reflected to the front within a predetermined range.
In addition, the LED light emitting apparatus 210 is disposed so that the orthogonal moving-away direction relative to first edge 201a of each LED chip 201 constitutes a directly rearward direction directed towards the reflector 242. As has been described above, the installing direction of the wire 209 extended from the pad electrode 202 disposed on the first edge 201a side of each LED chip 201 is the orthogonal moving-away direction relative to the first edge 201a of the LED chip 201. Consequently, the wire 209 enters in parallel an optical path directed rearwards from the LED chip 201 towards the reflector 242, generating a shadow of the wire 209. The shadow of the wire 209 then causes a problem that the quantity of light emitted from the LED chip 209 is reduced or an external appearance of the vehicle headlamp 240 is deteriorated as a result of the shadow being visible from an external location.
Patent Document 1 describes a vehicle headlamp in which light emitted upwards from light emitting surfaces of LED chips or to the peripheries thereof is reflected to the front by a reflector. However, bonding wires of the LED chips pass across a forward direction which is a light shining direction. In addition, there are described therein neither a form in which a plurality of pad electrodes are provided on the light emitting surfaces of the LED chips nor a form in which pad electrodes are provided in two diagonal corners of the light emitting surfaces of the LED chips, in particular. Patent Document 3 describes a form in which pad electrodes are provided in two diagonal corners of light emitting surfaces of LED chips. As a result of the LED chips being mounted obliquely on a substrate, bonding wires are installed in an inclined fashion. However, a problem described in the document as one that the invention is to solve is to perform smoothly a wire bonding operation, and hence, both the problem and configuration of that particular invention are different from those of this invention.    Patent Document 1: JP-A-2005-32661    Patent Document 2: JP-A-2006-245542    Patent Document 3: JP-A-2000-124508